Crude petroleum is a very complex mixture containing a wide range of hydrocarbons. It is converted into a diversity of fuels and chemicals through a variety of chemical processes in refineries. Crude petroleum is a source of transportation fuels as well as a source of raw materials for producing petrochemicals. Petrochemicals are used to make specialty chemicals such as plastics, resins, fibers, elastomers, pharmaceuticals, lubricants, and gels.
Branched hydrocarbons, branched fatty acids and other branched chain fatty acid derivatives (including branched fatty esters, branched fatty aldehydes, and branched fatty alcohols) are known to have additional preferred properties when compared to straight-chain molecules of same molecular weight (i.e., isomers), such as considerably lower melting points which can in turn confer lower pour points when made into industrial chemicals. These additional benefits allow the branched hydrocarbons, branched fatty acids, and other branched fatty acid derivates to confer substantially lower volatility and vapor pressure, and improved stability against oxidation and rancidity, thus making them particularly suited as components or feedstock of cosmetic and pharmaceutical applications, or as components of plasticizers for synthetic resins, solvents for solutions for printing ink and specialty inks, and industrial lubricants.
Such additional preferred properties can also be obtained in unsaturated fatty acid derivatives (including unsaturated hydrocarbons, unsaturated fatty acids, and other unsaturated fatty acid derivates), typically with high degrees of unsaturation, but unsaturation promotes oxidation and can lead to short shelf lives and corrosion problems. Therefore, lower melting points, pour points, volatility, and vapor pressure, as well as improved oxidative stability, are better obtained through branching.
Obtaining branched specialty chemicals from crude petroleum requires a significant financial investment as well as a great deal of thermal energy. It is also an inefficient process because frequently the long chain hydrocarbons in crude petroleum are cracked to produce smaller monomers. These monomers are then used as the raw material to manufacture the more complex specialty chemicals. Furthermore, in the petrochemical industry, it is commonplace to obtain branched chemicals, such as, for example, branched alkanes, branched alkenes, branched fatty acids, branched fatty esters, branched fatty alcohols and branched fatty aldehydes by isomerization of straight-chain hydrocarbons, using various catalytic processes. Expensive catalysts are typically employed in these processes, therefore increasing the costs of manufacturing. The catalysts that are used often become undesirable contaminants that must be removed from the finished products, thus adding further costs to the processes.
The most important transportation fuels—gasoline, diesel, and jet fuel—contain distinctively different mixtures of hydrocarbons which are tailored toward optimal engine performance. For example, gasoline comprises predominantly straight chain, branched chain, and aromatic hydrocarbons ranging from about 4 to 12 carbon atoms, while diesel predominantly comprises straight chain hydrocarbons ranging from about 9 to 23 carbon atoms. Diesel fuel quality is evaluated by parameters such as cetane number, kinematic viscosity, oxidative stability, and cloud point (Knothe G., Fuel Process Technol. 86:1059-1070 (2005)). These parameters, among others, are impacted by the hydrocarbon chain length as well as by the degree of branching or saturation of the hydrocarbon.
Microbially-produced fatty acids and other fatty acid derivatives (such as fatty esters, fatty alcohols, and hydrocarbons) can be readily tailored by genetic manipulation. Metabolic engineering enables microbial strains to produce different mixtures of fatty acids and other fatty acid derivatives, which can be optimized in meeting or exceeding fuel standards, and can be tailored to produce other chemicals or precursor molecules that are typically petroleum derived.
There is a need for cost-effective alternatives to petroleum products that do not require exploration, extraction, transportation over long distances, substantial refinement, and avoid the types of environmental damage associated with processing of petroleum. For similar reasons, there is a need for alternative sources of chemicals which are typically derived from petroleum. There is also a need for efficient and cost-effective methods for producing high-quality biofuels, fuel alternatives, and industrial chemicals from renewable energy sources.
Recombinant microbial cells engineered to produce branched chain fatty acids and other branched chain fatty acid derivatives, methods using these recombinant microbial cells to produce branched chain fatty acid derivatives, and compositions produced by these methods, address these needs.